One type of surface-mountable coil element is an inductor. In a power source line or a signal line, the inductor is used to, for example, eliminate noise.
Typically, a coil element has an insulator body, a coil conductor embedded in said insulator body, and an external electrode connected to an end portion of said coil conductor. Such a coil element is soldered to a circuit board via the external electrode.
The coil element presents a problem that magnetic flux that has penetrated an inside of the coil conductor leaks to an outside of said coil element, and the magnetic flux that has leaked to the outside (referred to as “leakage magnetic flux”) affects an operation of any other component.
There have been proposed coil elements intended to prevent or suppress leakage magnetic flux. For example, Japanese Patent Application Publication No. 2004-266120 discloses an inductor in which a magnetic path reinforcement layer 8 formed of iron foil is provided on a surface of a magnetic body 7 in which a coil 5 is embedded. The magnetic path reinforcement layer 8 is made of a magnetic material having a higher magnetic permeability than that of the magnetic body 7, and thus magnetic flux that has penetrated the coil 5 is guided to pass through the magnetic path reinforcement layer 8. As a result, magnetic flux is prevented from leaking to an outside of the inductor.
Furthermore, Japanese Patent Application Publication No. 2016-115935 discloses an inductor in which a metal magnetic plate 7 is provided in each of an upper portion and a lower portion of an insulator body 50 in which a coil is embedded. The metal magnetic plate 7 is made of a magnetic material having a larger magnetic permeability than a metal magnetic powder 51 contained in the insulator body 50, and thus magnetic flux that has penetrated the coil is prevented from leaking to an outside of said inductor.